1. Field of the Invention
This invention relates to computer assisted surgery generally and more specifically to orthopedic joint replacement surgery of the shoulder.
2. Description of the Related Art
Computer-aided tracking technology has been developed and successfully used for many types of surgical intervention. In orthopedic surgery, computer-aided tracking technology (i.e. navigation) has been developed for hip, knee, and spine surgery. One system for computer assisted hip navigation is described in U.S. Pat. No. 6,711,431 to Sarin, et al. (March 2004). Other reports of computer assisted surgical navigation are available in the medical and patent literature. Use of navigation technology in shoulder surgery is much more recent and less developed. One publication describes navigation in shoulder arthroplasty surgery, but that disclosure is limited to a method of orienting the humeral implant in treating shoulder fractures1. See Bicknell et al., “Computer-assisted Shoulder Hemiarthroplasty for fractures of the Proximal Humerus: an in vitro Comparison with Traditional Methods,” Fourth annual Meeting of the International Computer-Assisted Orthopaedic Society, (Chicago, 2004) pp. 131-132. Orientation of the glenoid component was not addressed in that publication.
FIG. 1 shows the skeletal structure of the human shoulder joint. This joint enables the Humerus 10 to pivot with respect to the Scapula 12. In total shoulder arthroplasty surgery, both the glenoid cavity 14 and humeral head 16 are replaced by prosthetic implants. The spatial orientation of these implants is a critical parameter that can determine surgical success and implant longevity. The glenoid component, in particular, must be properly oriented with respect to the scapula and to the humeral head in order to function correctly. One of the shoulder arthroplasty surgeon's primary intra-operative goals is achievement of correct glenoid component alignment and orientation.
Glenoid component orientation is defined in terms of two angular measurements: the inclination and version angles. Both angles are defined relative to planes of the scapula. Inclination is expressed in an anterior-posterior (front-to-back) projection of the scapula while version is expressed in an axillary (top-to-bottom) projection. Both inclination and version of the glenoid component are usually determined by the surgeon using manual instruments that prepare the native glenoid cavity for implantation. Typically, the surgeon uses visual cues and experience to determine the final orientation of the glenoid component. As in hip replacement surgery, such methods are not robust and frequently result in less than optimal orientations. The use of navigation in shoulder replacement surgery is expected to provide a significant clinical benefit, particularly due to improved orientation of the glenoid component.
Automated tracking devices and software have been developed which can assist in tracking and measuring individual bones in real time during surgery, as described in the Sarin patent referenced above and elsewhere. However, there is a need for specific devices and methods to apply such tracking techniques to shoulder replacement surgery.